1. Field of the Invention
The present invention is in the general field of surgical and endovascular interventional instruments, and relates particularly to intralumenal implants to occlude vessels or aneurysms. More specifically, the present invention relates to intralumenal implants for vascular lesions of vertebral bodies and/or intervertebral discs to gain disc stability and to eliminate discogenic pain.
2. Description of Related Art
There are a number of medical situations where it is desirable to occlude various elements of the vascular system. For example, vascular abnormalities such as arterio-venous malformation (AVM) and arterio-venous fistulae may form aneurysms that gradually increase in size only to eventually burst causing a catastrophic bleed particularly if the bleed occurs in the brain. Various metallic coils made of biocompatible elements such as platinum, gold and tungsten are presently used as intralumenal implants for occlusion of body arteries and veins, brain aneurysms, and vascular malformation. These radiopaque coils are typically placed at the desired site within a vascular lumen, percutaneously or through a microcatheter.
The coils occlude vessels or aneurysms by filling the lumen and acting as a physical barrier to blood flow. Ultimately the coils promote thrombus formation that further limits blood flow. Permanent occlusion of vessels or aneurysms requires the formation of an intralumenal thrombus that induces scar formation and the formation of neo-endothelium across the neck of aneurysms.
However, conventional coils are often not sufficient to form and mature thrombus the within aneurysms. As a result, conventional coils often do not appear to promote prompt endothelialization across the neck of aneurysms. This problem is most obvious in small aneurysms with a wide neck and in large or giant aneurysms. To solve this shortcoming of conventional intralumenal implants such as metallic coils, intralumenal implants of liquid embolic agents have been developed. One such material is composed of liquid cyanoacrylate monomer that rapidly polymerizes into a solid upon contacting a trace amount of water. Although cyanoacrylate can work rapidly it has certain drawbacks: 1) Polycyanoacrylate is so rigid to cause a harmful mechanical damage to surrounding soft vascular tissue; 2) both cyanoacrylate monomer and the byproducts of polymerization are toxic; 3) When cyanoacrylate is injected into a vascular by a catheter, there is no contact with water until the cyanoacrylate leaves the tip of the catheter where it instantly solidifies fixing the tip of the catheter and making withdrawal of the catheter difficult; 4) Because biologically active substances such as cytokines are not miscible with cyanoacrylate, it is impossible to load them into the occlusive agent. The last shortcoming is significant because biologically active substances play an important role of promotion of prompt endothelialization, which results in permanent stability of the injected embolic agents.
Another liquid embolic material is fibrin glue. The demerits of fibrin glue are: 1) In order to get fibrin glue to polymerize, a mixing process of fibrinogen aqueous solution and thrombin/calcium chloride aqueous solution is required, thereby making injection into a vascular lumen by catheter difficult; 2) The conversion from fibrinogen to fibrin is too slow for the injected fibrinogen to remain and turn to fibrin before being carried away by the blood flow; and 3) Fibrin glue is susceptible to metabolic destruction (e.g., by plasminogen) so it may not remain long enough for neo-endothelium formation.
Water-insoluble polymers dissolved in organic solvents have also been used as liquid embolic agents. The serious problems of these materials are: 1) Organic solvents such as dimethylsulfoxide are potentially toxic to the vascular walls and the surrounding tissues; and 2) Insolubility of biologically active substances in organic solvents makes loading of biologically active substances virtually impossible.
These problems common to the conventional liquid embolic agents, e.g., poor biocompatibility including toxicity and mechanical mismatching, poor durability, difficult injection mode and poor miscibility of biologically active substances with the conventional liquid embolic agents have hitherto remained unsolved.